Electronic device for electrical energy conversion between a voltage source and a current source by means of controllable switching cells

ABSTRACT

This invention relates to an electronic device for the conversion of electric energy between a voltage source E and a current source J. This device is comprised of cascaded switching cells (CL k ) each having two switches (I Ak , I Bk ) and comprising capacitors (C k ) associated with the cells for distributing the voltage of the source over the switches, and control logics (LG k ) which condition the exchanges of energy and are synchronized for limiting the voltage supported by each switch to a fraction (V/n) of the supply voltage, for limiting the ripple amplitude of the voltage of the output to the same fraction V/n and for conferring on this ripple voltage a frequency (nF) which is a multiple of the switching frequency (F) of the switches.

This invention relates to an electronic device for converting electric energy between a voltage source and a current source, comprising n controllable switching cells, each comprised of at least two switches working in a complementary manner, with n≧2.

BACKGROUND AND OBJECTS OF THE INVENTION

According to the definition provided in "Techniques de l'Ingenieur," Electronic Volume, pp D3-150 and following; by the term "voltage source" is meant an electric dipole (generator or receiver) of which the voltage at the terminals can not undergo a discontinuity by reason of the circuit exterior to said dipole (examples: storage battery, alternating distribution networks, high value capacitor . . . ); by the term "current source" is meant an electric dipole (receiver or generator) which is traversed by a current which cannot undergo a discontinuity by reason of the circuit external to said dipole (examples: inductive load, coil, direct current machine . . . ).

In a conventional manner, static converting devices are comprised of a combination of switching cells, each formed from two switches of complementary operation, that is, one being conducting when the other is blocked or non-conducting. Each cell has an associated control logic which assures the complementary status and manages the exchanges of energy as a function of the application.

A variation of these prior converting devices, known as a "three level converter" is known and has been in use since 1981 in the high voltage field (references: Ch. Bachle et al, "Requirements on the Control of a Three-Level Four Quadrant Power Converter in a Traction Application," Proceeding E.P.E. Aachen 1989, pp 577 to 582; B. Velaerts et al, "New Developments of 3-Level PWM Strategies," Proceeding E.P.E. Aachen 1989, pp 411 to 416.) Devices of this type are comprised of modules with four switches and these latter are imbricated to form two series, and no longer operate in a complementary manner. Two diodes are connected to a capacitative mid-point connected to the voltage source in order to limit the value of the voltages supported by each of the 4 switches to the half-voltage and to furnish three levels of voltage output, (from which comes the name "three level invertor" for these devices). A specific control is necessary in this type of device to permit the set of diodes to carry out its role of clipping and dividing the voltage, but this control is incompatible with a complementary operation of the switches of the two series. Under these conditions; such a device provides at the output a voltage wave in which the amplitude and the frequency are related:

this wave is accomplished either between the level of intermediate voltage and one of the extreme levels and thus has an amplitude which is only a fraction (V/2) of the overall supply voltage (V), the frequency of this wave being then equal to the control frequency (F) of the switches,

or this wave overlays the three voltage levels and thus has an amplitude equal to the overall supply voltage (V), but in this case, the frequency of this wave is a multiple of the control frequency of each switch (2F).

In the first case, the limited value (V/2) of the wave amplitude of the output voltage would tend to facilitate its filtering, but this would eliminate a low frequency F, which limits this advantage. Conversely, in the second case, the high frequency (2F) of the output voltage wave would tend to facilitate its filtering, but the high value of the amplitude thereof (V) limits this advantage. As a result, by their own nature, these devices do not permit benefitting from the advantages associated with a reduction of amplitude (V/2) and a multiplication of frequency (2F).

In other words, the very specific character of the control of these devices, the switches of which do not operate in a complementary manner, limits to four the number of switches which can make up a module.

It is to be noted that certain conventional converters (converters with greater pulse modulation) are comprised of combinations of switching cells which are arranged in parallel on the voltage source, with the current source connected between the switching cells. In these converters, the switches of each cell operate in a complementary mode (Patel and Hoft, "Generalized Techniques of Harmonic Elimination and Voltage Control in Thyristor Inverters," I.E.E.E. Transactions On Industry Applications, Vol. IA.9, n. 3, May-June 73). These devices may have the cumulative advantages indicated previously (conversion with reduced voltage and multiple frequency). However, in these converters; each switch must support the total overall supply voltage which, for high voltages, is a serious drawback with respect to prior devices in which the voltage at the terminals of each switch is a fraction (V/2) of the overall voltage (V). Moreover, the number of levels of voltage delivered at the output of these inverters is limited to three, and the multiplication of the frequency is limited to 2, regardless of the number of parallel cells.

DESCRIPTION OF THE INVENTION

The present invention seeks to provide an improved conversion apparatus, which combines the following advantages:

the possibility of placing in operation a high number of cells (n), this number may be equal to 2, but may also have a greater value (3 or more);

voltage carried by each switch equal to a fraction (V/n) of the overall supply voltage (V);

conversion of the output voltage with an amplitude limited to the fraction (V/n) of the total voltage,

frequency of this inversion which is a multiple of the switching frequency of each switch (F).

To this end, the device provided by the invention for the conversion of electrical energy between a voltage source and a current source comprises the following means:

-n- controllable stitching cells, each comprising two switches, with n≧2, each cell being marked by a rank k with 1≦k≦n,

a control logic connected to each switching cell for delivering to it control signals of a frequency F able to assure opposite switchings for the two switches of the cell,

control means adapted to deliver to the control logic a reference signal sr as a function of the desired energy conversion,

n homologous switching cells connected in series and n other homologous switches being themselves connected in series, in such a manner as to provide two symmetrical series, termed series A and series B, in which the two switches of each cell occupy symmetrical positions with respect to the current source,

the two series A and B of switches being interconnected, first, by a side common to the current source, and second, by their opposite sides common to the voltage source, the rank k associated with the cells increasing from the cell whose switches are directly connected or common to the current source (k=1) up to the cell whose switches are directly connected or common to the voltage source (k=n).

The device according to the present invention is characterized in that:

capacitors are associated with the switching cells in such a manner that the symmetrical terminals of the two switches of each cell are connected together through a capacitor for maintaining a voltage, called a capacitor charge voltage, between the terminals, and assuring an alternating circulation of current from one switch to the other switch of the cell,

the control logics of the n switching cells are synchronized for distributing their control signals over time in such a manner that the circulating current in each capacitor presents, in one period 1/F, an average value essentially proportional to the variation of the voltage at the terminals of the source voltage over this same period, and in particular essentially zero for a continuous voltage source.

As will be better understood below, the capacitors provided on the terminals of each cell support increasing fractions of the voltage from the source as a function of their rank. The difference between the charge voltages of these successive capacitors is thus equal to V/n, and it is this difference (V/n) which supports the two switches of the cell connected to the two capacitors considered. Moreover, the synchronization of the control logics permits obtaining a frequency (nF) of the output voltage wave which is a multiple of the control frequency (F) by reason of the shifts of the switchings of the n cells which are distributed over each period 1/F. In other words, this shift brings about the appearance of n distinct levels of output voltage (n levels distributed regularly over the period 1/F, two adjacent levels being separated by a voltage equal to V/n).

The operation of each cell is similar to that of the adjacent cell (at the nearby time shift) such that it is possible to readily understand in each application the control logics permitting management of the desired energy exchanges regardless of the number n of cells placed in the set (these control logics all being structurally analogous since the control signals which they deliver have the same motives and are deduced one from the other by a shift).

DESCRIPTION OF THE DRAWINGS

The description which follows in reference to the accompanying drawings shows the invention; in these drawings which form an integral part of the present description:

FIG. 1 is an electrical schematic view of the principle of the converting device of the invention, which shows its power portion and its control portion;

FIG. 2 shows one embodiment of the control portion of this device;

FIG. 3a illustrates the logic signals delivered to the two successive cells k and k+1;

FIGS. 3b and 3c illustrate respectively the behavior of the current traversing the capacitor C_(k) associated with the cell of rank k and the behavior of the voltage V_(ck) at the terminals of this capacitor;

FIG. 4 is an electronic schematic of one embodiment of the device of the invention in the case of a continuous voltage source and a continuous current source (clipped direct current);

FIG. 5 illustrates the trace of various signals relative to the control portion of the device;

FIG. 6 illustrates the trace of currents and voltages in the power portion of this device,

FIG. 7 illustrating the tracing of voltages at the capacitor terminals;

FIG. 8 is an electronic schematic of another embodiment in the case of a constant voltage source and a source of symmetric alternating current;

FIG. 9 illustrates the tracing of various signals relative to the control portion of this apparatus;

FIG. 10 illustrates the tracing off the currents and voltages in the power portion of this device,

FIG. 11 illustrating the tracing of voltages at the capacitor terminals;

FIG. 12 is a schematic view of a variation of the device of FIG. 8, provided with two switching cells;

FIGS. 13 and 14 illustrate the tracing of the signals of the device of FIG. 12;

FIG. 15 is an electronic schematic view of another embodiment in the case of an alternating voltage source and a constant current source;

FIGS. 16, 17, 18, 19, 20 and 21 illustrate the tracing of signals of the device of FIG. 15;

FIG. 22 is an electronic schematic view of another embodiment in the case of an alternating voltage source and an alternating current source;

FIGS. 23, 24, 25, 26 and 27 illustrate the tracing of signals of the device of FIG. 22.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The device shown in FIG. 1 comprises n switching cells CL₁, CL₂ . . . CL_(k) . . . CL_(n), n being any whole number greater than or equal to two. Each cell is composed of two switches symbolized as I_(Ak) and I_(Sk) which are controlled to have complementary states at each instant; these switches are preferably static semiconductor switches.

A series of n switches of the n cells are connected and constitute the A series of the device; the n other switches are connected and form the B series. The two series A and B of switches are interconnected, first, by a common extremity to a source of current J (according to the definition provided above), and second by their opposite extremities to the terminals of a voltage source E (according to the definition provided above). The cell CL₁ is directly connected to the source of current J, the other cells being more remote from the source as their rank k increases, until reaching the cell of rank n directly connected to the terminals of the voltage source E.

The current source J and the voltage source E may have different characteristics depending upon the application (continuous, alternating, generating, receiving). The stitches are selected as a function of these characteristics in such a manner that their reversibility of voltage is identical to that of the voltage source E and their reversibility of current is identical to that of the current source J.

At each switching cell CL_(k), there is associated a capacitor C_(k) which is connected between the symmetrical terminals of the two switches I_(Ak) and I_(Bk) of the cell CL_(k) under consideration, (the capacitor C_(k) of rank k being connected between the common terminal of the switches I_(Ak) and I_(Ak+1) of one part, and the common terminal of the switches I_(Bk) and I_(Bk+1) of the other part). The last cell CL_(n) may be associated with a specific capacitor C_(n) (shown in broken lines in FIG. 1) in the hypotheses in which the source E will not be a perfect voltage source in order to compensate for its imperfections. In the contrary case, a perfect source E plays the role of capacitor C_(n) with regard to the cell CL_(n).

The blocked switch (I_(Ak) in the example in the drawing) of the cell CL_(k) supports the difference in voltages V_(ck) -V_(ck-1) existing at the terminals of the two adjacent capacitors C_(k) and C_(k-1). Each capacitor has as its function to maintain at its terminals a voltage, called a load voltage V_(ck) of the capacitor; a distribution of these load voltages proportional to the rank of the capacitor V_(ck) =kV/n (V being the voltage at the terminals of the source E) assures at the terminals of the blocked switches a voltage difference V_(ck) -V_(ck-1) equal to V/n for all the blocked switches. According to the states of the switches of the two cells (CL_(k+1) and CL_(k), the capacitor C_(k) associated with the cell CL_(k) is traversed by a current i_(ck) equal to: +I, O or -I (I being the current which passes from the current source J). Each capacitor C_(k) is sized such that the voltage variations V_(ck) at its terminals are weak with respect to the voltage kV/n and in particular less than 0.2 V/n (the maximum voltage at the terminals of the blocked switches is then limited to 1.4 V/n).

In other words, each capacitor is selected to present a behavior under voltage as a function of its rank, greater than the value k·V_(max) /n, where V_(max) is the maximum value of the voltage V. It will be understood that the capacitors may be identical: they will then be sized to support the voltage V_(max) (which is susceptible of being applied to the latter between them).

In addition, the device comprises n control logics LG₁ . . . LG_(k), . . . LG_(n), one logic being connected to each switching cell for delivering to it the logic control signals sc₁, sc₂ . . . sc_(k) . . . sc_(n) of a frequency F able to assure the opposite switchings of the two switches of the cell at the frequency F.

Each logic, of a known structure, generally comprises a comparator and a matching circuit (a function of the type of switch which it controls), receives from the control means (shown in the drawings as a control generator GP) a reference signal sr either continuous (DC) or alternating (AC) which is a function of the energy conversion desired. This generator depends on the application and may, for example, furnish a reference signal commanding a regulation of current (current on output I of a given value regardless of the variations of the input voltage V).

The control logics LG_(k) may be structurally identical and it is by their synchronization that the shifted switchings of the cells CL_(k) are directed in order that:

the wave of the output voltage V_(s) has an amplitude equal to V/n and a frequency equal to nF, a multiple of the switching frequency F of the switches I_(Ak) and I_(Bk),

the voltage supported by each capacitor V_(ck) is equal to the fraction kV/n of the supply voltage V.

To this end, the control logics are connected to synchronization means SYNCHRO adapted to deliver to said logics synchronization signals sy₁ . . . sy_(k) . . . sy_(n) able to impose the law of distribution in time of the control signals sc_(k) issued by the logics LG_(k). This distribution of control signals permits controlling the voltage V_(ck) at the terminals of each capacitor such that the voltage is essentially proportional to its rank k (kV/n).

This result is obtained while controlling the current i_(ck) circulating in each capacitor such that it has, on one period 1/Ft an average value essentially proportional to the variation of the voltage at the terminals of the voltage source E over this same period, and in particular essentially zero for a continuous voltage source. This control may in particular be achieved while delivering to the control logics LG_(k) synchronization signals sy_(k) which condition the output of said logic control signals sc_(k) shifted with time, imposing logic states e_(k) and e_(k+1) of the adjacent cells of predetermined relative durations. The logic state e_(k) of one cell CL_(k) is defined as equal to 1 when the switch I_(Ak) of the cell forming part of the series A is passing (the other switch I_(Bk) of the cell, of the series B, being blocked), and equal to 0 when the switch of said A series is blocked (the other switch of the cell, of series B, being passing).

As will be seen from the examples which follow, the structure of the synchronization means depends upon the characteristics of the voltage source E and the current source J.

FIG. 2 explains one possible structure of the synchronization means SYNCHRO.

This synchronization means comprises in this example an oscillator OSC of a frequency F, and a succession of delay circuits RET_(k), which generate a system of n signals sd_(k) shifted for two successive signals of a time difference equal to 1/nF. These signals are corrected in n summers SM_(k) which each receive a correction signal sg_(k) and deliver at their output synchronization signals sy_(k). The correction signals sg_(k) are elaborated in correctors COR_(k), as data, the values of the voltage V and the current I. The correction signal sg_(k) delivered by each corrector COR_(k) is proportional to the rank k of the corrector, at the frequency F, at the variation of voltage V₀ -V₁ over the period 1/F, and at the capacitance of the capacitor of the same rank k, and inversely proportional to the average value I₀ +I₁ !/2 of the current over said period: ##EQU1##

These values of the correction signals sg_(k) assure the appropriate distribution of control signals sc_(k) issued by the logics LG_(k) and, as a consequence, the aforesaid distribution of voltages at the terminals of the capacitors and of the switches.

It should be noted that the correction which is produced in the foregoing example at the level of the synchronization means SYNCFRO may also (with an opposite sign) be on the reference signal sr issued by the control generator. The logics LG_(k) being comprised of comparators (according to the adjustment circuits), the two circuits are functionally equivalent and the invention defined in the case of one or the other circuit extends as well to the two.

FIG. 3a illustrates the tracing of the control signals sc_(k) and sc_(k+1) delivered by the control logics LG_(k) and LG_(k+1) to the two cells CL_(k) and CL_(k+1) (these signals represent the logic states e_(k) and e_(k+1) of these cells). These signals having a frequency F are shifted in time and have different periods (by reason of the corrective terms introduced).

Schematically shown in FIG. 3b is the tracing of the current I_(ck) in the capacitor C_(k), which alternatively takes the values +I, O, -I, according to the relative positions of the fronts of the signals sc_(k) and sc_(k+1) (I: current which passes from the current source, here assumed variable). The circulation of the current I_(ck) in the capacitor C_(k) causes a variation of the voltage V_(ck) at its terminals: the tracing thereof is illustrated in FIG. 3c. Over a period 1/F, the progression of the voltage V_(ck) is proportional to the variation in the voltage V over the same period and to the rank k of the capacitor: V_(ck) remains close at each instant to the value kV/n.

FIG. 4 is an example of the aforementioned embodiment in the case of a source E of continuous voltage and a source J of continuous current through all of the figures of the drawings, at the ends, in order to facilitate understanding thereof, the same references have been repeated for similar elements).

In this example which comprises three switching cells, the switches I_(A1), I_(A2), I_(A3) of the A series are switches of the type which are controllable at the start and upon blocking, in particular bipolar transistor type (or even Darlington, MOST, GTO or IGBT transistors). The switches I_(B1), I_(B2), I_(B3) of the B series are spontaneous double switching switches, i.e. diodes.

In this application, the synchronization means is adapted in such a manner that the control signals sc_(k), sc_(k+1) delivered to two cells of successive ranks k and k+1 impose on these cells logic states e_(k) and e_(k+1) such that, if e_(k) ≠e_(k+1), the cumulative periods during which e_(k) ET e_(k) +1 =1 will be essentially equal to the cumulative periods during which e_(k) k ET e_(k+1) =1.

To this end, the synchronization means SYNCHRO comprises means for generating triangular phase shifted signals, comprised in the example shown by a triangular signal general OSCT which delivers a signal sd₃ of a frequency F the tracing of which is shown in FIG. 5, and for a phase shifter RET₂ of which the output is connected to another phase shifter RET₁. The phase shifters introduce a phase shift of 2π/n, thus in the example 2π/3. The signals issued from the generator OSCT (sd₃), from the phase shifter RET₂ (sd₂) and from the phase shifter RET₁ (sd₁) have relative phases of 0, 2π/3 and 4π/3, and are delivered respectively toward the logic control comparators LG₃, LG₂, LG₁. The control generator GP delivers as before the reference signal sr to the other input of the comparators. In the continuous/continuous application, the signal sr is continuous and varies as a function of the exchange of energy desired.

At the output of the comparators LG₃, LG₂, LG₁ appear the three control signals sc₃, sc₂, sc₁ comprised of the logic signals, of a value 1 when sd_(k) <sr, and a value of 0 in the opposite case.

These signals are delivered after adjustment on the control electrode of the switches IA₃, IA₂, IA₁.

FIG. 6 shows the tracing of the currents ic₁, ic₂ which. traverse the capacitors C₁ and C₂ (the voltage source E is assumed perfect playing the role of the capacitor C₃). It may be verified that, when two successive cells are in different states e_(k) and e_(k+1), there is circulation of current I from the source J in one direction or the other, through the capacitor situated between the two cells concerned. On the contrary, the current in this capacitor is zero when the two cells are in the identical states.

The last diagram of FIG. 6 shows the output voltage V_(s). This voltage has a wave with frequency 3F and amplitude E/3: these two conditions facilitate filtering of this voltage.

FIG. 7 illustrates the equilibrium of the voltages V_(c1) and V_(c2) at the terminals of the capacitors C₁ and C₂ by comparison of the continuous voltage V at the terminals of the voltage source E. It has been verified that the voltage V_(ck) at the terminals of a capacitor k is essentially equal to kV/n (here kV/3).

The voltage at the terminals of a switch I_(Ak) or I_(BK) (V_(IAK) or V_(IBK)) is either zero or equal to the difference in the voltages at the terminals of the two capacitors C_(k-1) C_(k) which surround it. It then follows that this voltage is limited to V/n (here V/3).

FIG. 8 is an example of an embodiment in the case of a source E of continuous voltage and a source J of symmetrical alternating current of a frequency fi (the frequency F of the switches being notably greater than the frequency fi). This example corresponds to a voltage inverter (direct/alternating converter) or, according to the reversibility, a current rectifier (alternating/direct converter).

In the example shown which also comprises three cells (but which may be generalized as n cells) all the switches I_(A1), I_(A2), I_(A3), I_(B1), I_(B2), I_(B3) are of the same type, reversible with respect to the current and unidirectional with respect to the voltage. In FIG. 8, they are comprised of double bipolar transistors, each with a non-parallel diode. Each of these bipolar transistors may be replaced, depending upon the applications, by a Darlington, MOST, GTO, IGBT . . . transistor.

In this application, the synchronization means SYNCHRO is adapted in such a manner that the control signals sc_(k), SC_(k+1) delivered to the two cells CL_(k), CL_(k+1) of successive ranks k and k+1 impose on these cells logic states e_(k) and e_(k+1) such that:

the logical size e_(k) ET e_(k+1) is periodic, of a frequency 2fi, double the frequency of the current source J,

the logical size e_(k) ET e_(k+1) is equal periodic, with the same frequency 2fi.

To this effect, the control means GP is adapted to deliver a symmetrical alternating reference signal sr of frequency fi. Moreover, the synchronization means comprises means for generating symmetrical alternating triangular signals sd_(k), composed in the example of n generators OSCT, RET₂, RET₁, corresponding to -n- cells and assign the same rank, the generators having the same amplitude and the same frequency -F- which is a multiple of the frequency fi for delivering triangular signals shifted in time such that the signal Sd_(k+1) issued by the generator of rank k+1 is retarded in time by a value of 1/nF with respect to that of sd_(k) issued by the generator of rank k.

The n logics LG_(k) are each comprised of a comparator connected to the control means GP and to a triangular signal generator, the comparator which is connected to the generator of rank k being connected to the switching cell of rank k for controlling the same as a function of the relative values of the two signals (sd_(k), sr) which it receives.

As previously, the triangular signal generators may be comprised of an oscillator OSCT and a series of phase shifters RET_(k) 2π/n in such a manner as to deliver triangular signals shifted by 2π/n for a signal with respect to the succeeding signal.

At the output of the comparators LG₃, LG₂, LG₁ of the control logics, appear control signals sc₃, sc₂, sc₁ which have characteristics similar to those already described above. These signals which are represented in FIG. 9 are delivered to the switches I_(A1), I_(A2), I_(A3). The conditions already explained in the preceding embodiment are verified in this case. After inversion and galvanic isolation in the circuits INV_(k), these signals assure the control of the three other switches I_(B3), I_(B2), I_(B1).

FIG. 10 shows the tracing of the currents which pass through the capacitors C₁ and C₂. The same comments as in the preceding case may be formulated here. The last diagram of FIG. 10 shows the voltage of the output V_(s) : as before, this voltage has a ripple frequency nF and amplitude E/n (n=3 in the case shown of three cells).

FIG. 11 illustrates the equilibrium of the voltages at the terminals of the capacitors: the voltage V_(ck) at the terminals of the capacitor of rank k is essentially equal to kV/n. In other words, in this case as well, the voltage at the terminals of a switch is limited to V/n (here V/3).

FIG. 12 shows a variation of the device shown in FIG. 8 (source of continuous voltage E and source of symmetrical alternating current of frequency fi). In the device of FIG. 12, the number n of cells is equal to 2 and the switching frequency F is equal to the frequency fi of the current source. The power portion of the device is similar to that of FIG. 8. The reference signal sr issued by the control generator is treated in the control logic LG₂ associated with the second cell in such a manner as to deliver a control signal sc₂ of a frequency fi. This control logic LG₂ may for example be comprised of a memory device storing predefined control commands which are read at the frequency F=fi and selected as a function of the signal sr. This signal which serves to control the cell CL₂ (after inversion for the switch of the series B) is received by the logic LG₁ attached to the cell CL₁ in order to deliver a control signal sc₁ to said cell CL₁. The control signals sc₁ and sc₂ impose on these cells logic states e₁ and e₂ such that e₂ is obtained in complement to e₁ and while shifting it one half-period 1/2F.

To this end, the logic LG₁ may in particular be comprised of an inverter followed by a π phase shifter DEPH. As the case may be, the signal sc₁ may be stored (as the signal sc₂) in memory for being read at the frequency F=fi.

FIG. 13 illustrates the control signals sc₂ and sc₁. The last diagram of this figure illustrates in dashed lines the current I of the source J and in solid lines, the current I_(c1) circulating in the capacitor C₁. It is noted that this current has an average value of zero.

FIG. 14 illustrates the tracing of the voltage V_(s) at the output of the system (which is a three level voltage). The voltage V_(c1) at the terminals of the capacitor C₁ is therefor essentially equal to V/2 and the voltage at the terminals of the switch I_(A1) is limited to V/2.

FIG. 15 is an example of an embodiment of the device in the case of a symmetrical alternating voltage source E of a frequency fv, and a continuous current source J (the frequency F of the switchings being notably greater than this frequency fv). This example corresponds to an alternating/continuous and/or a continuous/alternating converter (rectifier or reversible current inverter).

In the example shown which comprises three cells (but which may be generalized as n cells), all of the switches I_(A1), I_(A2), I_(A3), I_(B1), I_(B2), I_(B3) are of the same type, reversible with respect to voltage and unidirectional as to current. In FIG. 15, they are comprised of bipolar transistors each arranged in series with a diode. Each of these transistors may be replaced depending upon the applications, by a Darlington, MOST, GTO (not necessarily needing a series diode), IGBT . . . transistor.

In this application, the synchronization means is adapted such that the control signals sc_(k), sc_(k+1) delivered to the two cells CL_(k), CL_(k+1) of the successive ranks k and k+1 impose on these cells logic states e_(k) and e_(k+1) such that, for each period 1/F, the difference between the duration of the state e_(k) AND e_(k+1) =1 and the duration of the state e_(k) AND e_(k+1) is essentially equal to ##EQU2##

where c_(k) is the capacitance of the capacitor of rank k,

I is the value of the current at the current source,

V₀ is the voltage at the terminals of the voltage source at the beginning of the period 1/F considered, and V₁ is this voltage at the end of said period.

To this end, the control means is adapted to deliver a reference signal sr of alternative symmetry of frequency fv, which is illustrated in FIG. 16. Moreover, the synchronization means SYNCHRO comprises:

means for generating n triangular signals of alternative symmetry sd_(k), composed in the example of n generators OSCT, RET₂, RET₁, corresponding to n cells and assuming the same rank, the generators having the same amplitude and the same frequency -F- which is a multiple of the frequency fv for delivering triangular signals shifted over time such that the signal sd_(k+1) issued from the generator of rank k+1 is delayed in time by a value 1/nF with respect to signal sd_(k) issued from the generator of rank k (FIG. 17),

correctors COR_(k) corresponding to the cells and assigned the same rank, each corrector being connected to the control means and adapted to deliver a corrected reference signal sg_(k) of a relative amplitude g_(k) with respect to that of the triangular signals sd_(k), such that ##EQU3##

The logics LG_(k) are each comprised of a comparator receiving a triangular signal sd_(k) and receiving a corrected reference signal sg_(k), the comparator which is connected to the generator of rank k being connected to the switching cell of rank k for controlling the same as a function of the relative values of the two signals sd_(k), sg_(k) which it receives.

The corrected reference signals sg_(k) are illustrated in FIG. 18.

As before, the triangular signal generators may be comprised of an oscillator OSCT and a succession of phase shifters RET_(k) 2π/n in such a manner as to deliver triangular signals shifted by 2π/n for a signal with respect to the following one.

As the output of the comparators LG₃, LG₂, LG₁ of the control logics, appear the control signals sc₃, sc₂, sc₁ which have similar characteristics to those described previously. These signals which are shown in FIG. 19 are delivered to the switches I_(A3), I_(A2), I_(A1). The conditions already described in the previous embodiments are verified in the present case. After inversion and galvanic isolation in the circuits INV_(k), these signals assure the control of the three other switches I_(B3), I_(B2), I_(B1).

FIG. 20 shows a tracing of the current I_(c1) which passes through the capacitor C₁ and that of the voltage V_(c1) at its terminals.

It is to be noted that the current I_(c1) presents an average value not zero, appropriate for provoking a variation of the voltage V_(c1) proportional to the variation of the voltage V at the terminals of the source E. The macroscopic variation of the voltage V_(c1) is better illustrated in FIG. 21. This figure shows also that the voltages V_(ck) at the terminals of the capacitors varies proportionally to their rank k.

FIG. 22 is an example of an embodiment of the device in the case of a source E of symmetrical alternating voltage of a frequency fv and a source J of symmetrical alternating current fi (the frequency F of the switchings being notably greater than the frequency fi and fv). This example corresponds to an alternating/alternating converter (for example a frequency changing converter designated as a "cycloconverter").

In the example shown which comprises three cells (but which may be generalized as n cells), all of the switches I_(A1), I_(A2), I_(A3), I_(B1), I_(B2), I_(B3) are of the same type, reversible with respect to voltage and current. In FIG. 22, they are comprised of bipolar transistors associated per pair in anti-series manner, each being provided with a diode in anti-parallel. Each of these transistors may be replaced, according to the applications, by a Darlington, MOST (the diode may be the internal diode of the MOST), GTO, IGBT . . . transistor.

In this application, the synchronization means SYNCHRO is adapted in such a manner that the control signals sc_(k), sc_(k+1) delivered to the two cells CL_(k), CL_(k+1) of successive ranks k and k+1 impose on these cells logic states e_(k) and e_(k+1) such that, over each period 1/F, the difference between the period of the state e_(k) AND e_(k+1) =1 and the period of the state e_(k) AND e_(k) +1=1 are essentially equal to: ##EQU4##

where c_(k) is the capacitance of the capacitor of rank k,

I₀ and V₀ are the values of the sources of current and voltage at the start of the period 1/F considered, and

I₁ and V₁ are these values at the end of said period.

The control means GP delivers a reference signal sr adapted to control the exchange of energy. In the example shown, this reference signal is of alternating frequency fv. The synchronization means SYNCHRO comprises:

means for generating triangular signals of alternating symmetry sd_(k), comprised in the example by n generators OSCT, RET₂, RET₁, corresponding to -n- cells and assumed to be the same rank, the generators having the same amplitude and a same frequency -F- (notable greater than the frequencies fi and fv), said generators being shifted in time such that the triangular signal sd_(k++1) issuing from the generator of rank k+1 is delayed in time by a value of 1/nF with respect to the signal sd_(k) issued by the generator of rank k (FIG. 24),

correctors COR_(k), corresponding to the cells and assumed to be of the same rank, each corrector being connected to control means GP and adapted to deliver a corrected reference signal sg_(k) of a relative amplitude g_(k) with respect to that of the triangular signals sd_(k), such that ##EQU5##

The n logics LG_(k) are each comprised of a comparator receiving a triangular signal sd_(k) and a corrected reference signal sg_(k), the comparator which is connected to the generator of rank k being connected to the switching cell CL_(k) of rank k for controlling the same as a function of the relative values of the signals sd_(k), sg_(k) which it receives.

The triangular signals sd_(k) issued from the generators and the corrected reference signals sg_(k) are illustrated in FIG. 24.

As before, the triangular signal generators may be comprised by an oscillator OSCT and by a succession of phase shifters RET_(k) 2π/n for one signal relative to the successive one.

At the output of the comparators LG₃, LG₂, LG₁ of the control logics; appear control signals sc₁, sc₂, sc₃ which have characteristics similar to those already described previously. These signals which are shown in FIG. 25 are delivered to the switches I_(A3), I_(A2), I_(A1). The conditions already described in the preceding embodiments are verified in the present case. After inversion and galvanic isolation in the circuits INV_(k), these signals assure the control of the three other switches I_(B3), I_(B2), I_(B1).

FIG. 26 shows the tracing of the current I_(c1) which traverses the capacitor C₁ and that of the voltage V_(c1) at its terminals.

It is to be noted that the current I_(c1) has an average value not zero, appropriate to cause a variation of the voltage V_(c1) proportional to the variation of the voltage V at the terminals of the source E. The macroscopic variation of the voltage V_(c1) is better seen in FIG. 27. This figure shows as well the voltages V_(ck) at the terminals of the capacitors varying proportionally according to their rank k. 

We claim:
 1. An electronic device for the conversion of electric energy between a voltage source and a current source, comprisingn controllable switching cells (CL₁ . . . CL_(k) . . . CL_(n)) each comprising two switches (I_(Ak), I_(Bk)) with n≧2, each cell being identified by a rank k such that 1≦k≦n, a control logic (LG_(k)) connected to each switching cell (CL_(k)) for delivering thereto control signals (sc_(k)) of a frequency F, for assuring opposed switchings of the two switches of the cell, control means (GP) for delivering to said control logic a reference signal (sr) as a function of the energy conversion desired, -n- homologous switches of the cells being connected in series and the -n- other homologous switches themselves being connected in series, in such a manner as to provide two symmetrical series, termed series A and series B, in which the two switches (I_(Ak), I_(Bk)) of a given cell occupy symmetrical positions with respect to the source of current, the two series A and B of switches being interconnected by one common extremity to said current source (J), and by the other common extremity to said voltage source (E), the rank k associated with the cells increasing from the cell (CL₁) in which the switches are directly connected to the current source (k=1) to the cell (CL_(n)) in which the switches are directly connected to the voltage source (k=n), said conversion device being characterized in that: capacitors (c_(k)) associated with the switching cells (CL_(k)) in such a manner that the symmetrical terminals of the two switches (I_(Ak), I_(Bk)) of each cell are connected to each other through a capacitor for maintaining between said terminals a voltage, termed a load voltage of the capacitor, and assuring an alternate circulation of current from one switch to another switch of the cell, the control logics (LG_(k)) of the -n- switching cells are synchronized for distributing the control signals (sc_(k)) over time such that the current circulating in each capacitor (c_(k)) has, over a period of time 1/F, an average value essentially proportional to the variation of the voltage at the terminals of the voltage source over that same period of time, and in particular essentially zero for a continuous voltage source.
 2. A device as in claim 1, characterized in that each capacitor (c_(k)) associated with a switching cell (CL_(k)) has a range of voltage greater than a threshold V_(ck) as a function of increasing rank k of the cell with which is associated said capacitor, with V_(ck) =k.Vm/n where Vm is the maximum voltage of the voltage source (E).
 3. A device as in claim 1, characterized in that each capacitor (c_(k)) associated with the switching cell (CL_(k)) of rank k is sized so as to present a capacity c_(k) sufficient that variations of voltage at the terminals of said capacitor will be less than 0.2 V/n, where V is the voltage of the voltage source (E).
 4. A device as in claim 1, wherein the switches (I_(Ak), I_(Bk)) of the switching cells (CL_(k)) are static semiconductor switches, having a reversibility of voltage identical to that of the voltage source (E) and a reversibility of current identical to that of the current source (J).
 5. A device as in claim 1, characterized in that the control logics (LG_(k)) are connected to synchronization (SYNCHRO) comprising an oscillator (OSC) of a frequency F, a succession of delay circuits (RET_(k)) delivering a system of signals (sd_(k)) shifted for two successive signals by a time difference equal to 1/nF, correctors (CO_(k)) delivering correction signals (sg_(k)) proportional to the rank k of the corrector, at the frequency F, at the variation of voltage V₀ -V₁ over the period 1/F, and at the capacity of the capacitor of the same rank k, and inversely proportional to the average value ##EQU6## of current over said period, and totalizers (SM_(k)) for delivering synchronization signals (sy_(k)) from said shifted signals (sd_(k)) and said correction signals (sg_(k)), each control logic comprising a comparator receiving the reference signal (sr) issues by the control means (GP) and the synchronization signal (sy_(k)) of corresponding rank k issued by the synchronization means (SYNCHRO).
 6. A device as in claim 1, connected to a continuous voltage source and a continuous current source, for providing a continuous/continuous converter, in which each switching cell (CL_(k)) comprises an switch (I_(Ak)) of the type controllable upon starting and upon blocking, and a double spontaneous switching switch (I_(Bk)).
 7. A device as in claim 6, characterized in that the control logics (LG_(k)) of -n- switching cells are synchronized in such a manner that the control signals (sc_(k), sc_(k+1)) delivered to the two cells (CL_(k), CL_(k+1)) of successive ranks k and k+1 imposed on these cells logic states e_(k) and e_(k+1) such that, if e_(k) ≠e_(k+1), the cumulative periods during which e_(k) ET e_(k+1) =1 are essentially equal to the cumulative periods during which e_(k) ET e_(k+1) =1, the logic state e_(k) of one cell (CL_(k)) being defined as equal to 1 when the switch (I_(Ak)) of the cell forming a part of the series A is conducting (the other switch (I_(Bk)) of the cell, of the B series, being blocking), and is equal to 0 when the switch (I_(Ak)) of the A series is blocking (the other switch (I_(Bk)) of the cell of the B series being conducting).
 8. A device as in claim 7, characterized in that the control logics (LG_(k)) of -n- switching cells are connected to synchronization means (SYNCHRO) comprising means for generating triangular phase shifted signals (OSCT, RET₂, RET₁) able to deliver control signals (sd₃, sd₂, sd₁) of the same frequency -F- phase shifted by 2π/n for one signal relative to the following signal.
 9. A device as in claim 1, connected to a continuous voltage source and a source of symmetrical alternating current for providing a continuous/alternating and/or alternating/continuous converter in which each switching cell (CL_(k)) comprises two identical switches (I_(Ak), I_(Bk)) reversible as to current and unidirectional as to voltage.
 10. A device as in claim 9 connected to a constant voltage source and a source of symmetrical alternating current of a frequency fi, characterized in that the control logics (CL_(k)) of the -n- switching cells are synchronized in such a manner that the control signals (sc_(k), sc_(k+1)) delivered to the two cells (CL_(k), CL_(k+1)) of successive ranks k and k+1 impose on these cells logic states e_(k) and e_(k+1) such that:the logical value e_(k) ET e_(k+1) is periodic, of a frequency 2fi, twice the frequency of the source of current, the logical value e_(k) ET e_(k+1) is also periodic, with the same frequency 2 fi, the logic state e_(k) of one cell being defined as equal to 1 when the switch (I_(Ak)) of the cell forming a part of the A series is conducting (the other switch I_(Bk)) of that cell, of the B series, being blocking), and equal to 0 when the switch of said A series is blocking (the other switch of that cell, of the B series, being conducting).
 11. A device as in claim 10, characterized in that the control means (GP) is adapted to deliver a symmetrically alternating reference signal (sr) of a frequency fi, andthe control logics (LG_(k)) of the -n- switching cells are connected to synchronization means (SYNCHRO) comprising means for generating triangular signals (OSCT, RET₂, RET₁) adapted to deliver n symmetrical alternating triangular signals (sd_(k)), said signals having the same amplitude and the same frequency -F- as a multiple of the frequency fi and being shifted in time such that the states (sd_(k+1)) of the rank k+1 is delayed in time by a value of 1/nF with respect to the signal (sd_(k)) of rank k, the n logics (LG_(k)) each comprising a comparator receiving the reference signal (sr) issued by the control means (GP) and a triangular signal (sd_(k)) issued by the generation means, the comparator of rank k being connected to the switching cell (CL_(k)) of rank k for controlling the same as a function of the relative values of the two signals (sr, sd_(k)) which it receives.
 12. A device as in claim 9 connected to a constant voltage source and a source of symmetrical alternating current of a frequency fi, comprising two switching cells (LG₁, LG₂ ; n=2), characterized in that the control logics (LG₁ m LG₂) of the two switching cells are adapted such that the control signals (sc₁, sc₂) have a frequency P equal to the frequency fi of the current source, said logics being synchronized in such a manner that these control signals impose on the cells (CL₁, CL₂) logic states e₁ and e₂ such that e₂ is obtained in complement to e₁ and while shifting it one-half of a period 1/2F.
 13. A device as in claim 1, connected to a source of symmetrical alternating voltage having a frequency fv and a source of direct current for providing alternating/continuous and/or a continuous/alternating converter in which each switching cell (CL_(k)) comprises two identical switches (I_(Ak), I_(Bk)) reversible as to voltage and unidirectional as to current.
 14. A device as in claim 13, connected to a source of symmetrical alternating voltage having a frequency fv and a source of direct current, characterized in that the control logics (LG_(k)) of the -n- switching cells are synchronized in such a manner that the control signals delivered to the two cells (CL_(k), CL_(K+1)) of successive ranks k and k+1 impose on these cells logic states e_(k) and e_(k+1) such that over each period 1/F, the difference between the duration of the state e_(k) ET e_(k+1) =1 and the duration of the state e_(k) ET e_(k+1) =1 are essentially equal to ##EQU7## where C_(k) is the capacitance of the capacitor of rang k, I is the value of the current from the current source,V₀ is the voltage at the terminals of the voltage source at the start of the period 1/F considered, and V₁ is this voltage at the end of said period, the logic state e_(k) of a cell (CL_(k)) being defined as equal to 1 when the switch (I_(Ak)) of the cell forming a part of the A series is conducting (the other switch (I_(Bk)) of the cell, of the B series being blocking), and equal to 0 when the switch of said A series is blocking (the other switch of the cell, of the B series, being conducting).
 15. A device as in claim 14, characterized in that the control means (GP) is adapted to deliver a symmetrical alternating reference signal (sr) of a frequency fv, and in that the control logics (LG_(k)) of the -n- switching cells are connected to synchronization means (SYNCHRO) comprising:means for generating triangular signals (OSCT, RET₂, RET₁) adapted to deliver n symmetrical alternating triangular signals (sd_(k)), said signals having the same amplitude and the same frequency -F- as a multiple of the frequency fv and being shifted in time such that the signal (Sd_(k+1)) of rank k+1 is delayed in time by a value of 1/nP with respect to the signal (sd_(k)) of rank k, correction means (COR_(k)) for receiving the reference signals (sr) issued by the control means (GP) and adapted to deliver corrected reference signals (sg_(k)) of relative amplitude g_(k) with respect to that of the triangular signals (sd_(k)), such that ##EQU8## the n logics (LG_(k)) each comprising a comparator receiving a triangular signal (sd_(k)) and a corrected reference signal (sg_(k)), the comparator of rank k being connected to the switching cell (CL_(k)) of rank k for controlling the same as a function of the relative values of the two signals (sd_(k), sg_(k)) which it receives.
 16. A device as in claim 1, connected to a source of symmetrical alternating voltage and to a source of symmetrical alternating current for providing an alternating/alternating converter, in which each switching cell (CL_(k)) comprises two identical switches (I_(Ak), I_(Bk)) reversible as to current and voltage.
 17. A device as in claim 16, connected to a symmetrical alternating voltage source having a frequency fv and a symmetrical alternating current source having a frequency fi, characterized in that the control logics (LG_(n)) of the -n- switching cells are synchronized in such a manner that the control signals (sc_(k), sc_(k+1)) of successive ranks s_(k) and s_(k+1) impose on these cells logic states e_(k) and e_(k+1) such that, for each period 1/F, the difference between the duration of the state e_(k) +e_(k+1) =1 and the duration of the state e_(k) +e_(k+1) =1 is essentially equal to ##EQU9## where c_(k) is the capacitance of the capacitor of rank k, I₀ and V₀ are the values of the sources of current and of voltage at the start of the period 1/F considered, and I₁ and V₁ are these values at the end of said period, the logic state e_(k) of one cell being defined as equal to 1 when the switch (I_(Ak)) of the cell forming a part of the A series is conducting (the other switch (I_(Bk)) of the cell, of the B series, being blocking), and equal to 0 when the switch of the A series is blocking (the other switch of the cell, of the B series, being conducting).
 18. A device as in claim 17, characterized in that the control logics (LG_(k)) of the -n- switching cells are connected to synchronizing means (SYNCHRO) comprising:means for generating triangular signals (OSCT, RET₂, RET₁) adapted to deliver n symmetrical alternating triangular signals (SD_(k)), said signals having the same amplitude and the same frequency -F- greater than the frequencies fi and fv and being shifted in time such that the signal (sd_(k+1)) of rank k+1 is delayed in time by a value of 1/nF with respect to the signal (sd_(k)) of rank k, correction means (COR_(k)) receiving the reference signal (sr) issued by the control means (GP) and adapted to deliver corrected reference signals (sg_(k)) of a relative amplitude g_(k) with respect to that of the triangular signals (sd_(k)), such that ##EQU10## the n logics (LG_(k)) each comprising a comparator receiving a triangular signal (sd_(k)) and a corrected reference signal (sg_(k)), the comparator of rank k being connected to the switching cell (CL_(k)) of rank k for controlling the same as a function of the relative values of the two signals (sd_(k), sg_(k)) which it receives.
 19. A device as in claim 1, comprising two switching cells.
 20. A device as in claim 1, comprising three switching cells. 